array_map_recursive.php

<?php declare(strict_types=1);

if (!\function_exists('array_map_recursive')) {
    function array_map_recursive(array $array, callable $function): array
    {
        $out = [];
        foreach ($array as $key => $value) {
            $out[$key] = \is_array($value)
                ? array_map_recursive($value, $function)
                : \call_user_func($function, $value, $key);
        }
        return $out;
    }
}

memoize_mockingbird_functional_programming.php

<?php declare(strict_types=1);

/**
 * @see http://raganwald.com/2018/08/30/to-grok-a-mockingbird.html
 */

function memoize(\Closure $function): \Closure
{
    static $lookup = [];
    return function (...$args) use ($function, &$lookup) {
        $key = \sha1(\json_encode(\array_map_recursive($args, function ($value) {
            return \is_object($value) ? \spl_object_hash($value) : $value;
        })));
        return $lookup[$key] ?? ($lookup[$key] = $function(...$args));
    };
}

function mockingbird(\Closure $function): callable
{
    return function (...$args) use ($function) {
        return $function($function, ...$args);
    };
}

$exponent = function (\Closure $self, int $x, int $n): int {
    if ($n === 0) {
        return 1;
    } elseif ($n % 2 === 1) {
        return $x * $self($self, $x * $x, (int) \floor($n / 2));
    } else {
        return $self($self, $x * $x, $n / 2);
    }
};

$exp = mockingbird(memoize($exponent));

echo $exp(2, 8) . \PHP_EOL;
echo $exp(2, 8) . \PHP_EOL;
echo $exp(2, 9) . \PHP_EOL;
echo \PHP_EOL;

unflatten.php

<?php declare(strict_types=1);

if (!\function_exists('unflatten')) {
    /**
     * Takes a flat array (such as from an SQL result set) and unflattens it according to dot-notation, such as:
     * ['username' => 'admin', 'metadata.created' => '2018-04-24', 'metadata.updated' => '2018-09-17']
     *
     * [
     *     'username' => 'admin',
     *     'metadata' => [
     *         'created' => '2018-04-24',
     *         'updated' => '2018-09-17',
     *     ],
     * ]
     */
    function unflatten(array $array): array
    {
        $out = [];
        foreach ($array as $dotNotation => $value) {
            if (!\is_string($dotNotation)) {
                $out[$dotNotation] = $value;
                continue;
            }
            $keys = explode('.', $dotNotation);
            while ($key = \array_pop($keys)) {
                $value = [$key => $value];
            }
            $out = \array_merge_recursive($out, $value);
        }
        return $out;
    }
}